The present invention relates to a glass fiber having a third order nonlinear optical effect useful for an ultrafast speed optical switch or a wavelength conversion device.
To realize an advanced information processing society or multimedia, it is necessary to process a large quantity of information at an ultrafast speed, and for this purpose, an optical technology is indispensable which takes the place of conventional electronics processing. To realize such optical processing technology, various developments have been made on optical switches to process optical signals by means of light. To operate such optical switches, the third order nonlinear optical effect is utilized whereby the optical properties such as the refractive index and the transmittance of a material can be changed by light.
Further, as a system to increase the transmission capacity, a wavelength division multiplexing communication system (WDM) has been proposed. In this system, in order to increase the transmission capacity, the channel is multiplexed by changing the wavelength. Accordingly, in this system, it is desired that the wavelength conversion from a certain wavelength to other wavelength is easy, and for this purpose, four wave mixing is suitable which utilizes the third order nonlinear optical effect.
The four wave mixing means that when a pumping light having an angular frequency of xcfx89p and a signal light having an angular frequency of ws enter a third order nonlinear optical material, a light having an angular frequency of xcfx89c (=2xcfx89pxe2x88x92xcfx89s) will be generated. By such four wave mixing, the signal light having an angular frequency of xcfx89c will be converted to the light having an angular frequency of xcfx89c. If the third order nonlinear optical effect of the third order nonlinear optical material is large, this angular frequency conversion i.e. the wavelength conversion can effectively be carried out.
A third order nonlinear optical glass so-called a nonresonant type, accompanying no light absorption, such as quartz glass, is known to show a nonlinear response at a high speed of a few picoseconds or less. However, as compared with a third order nonlinear optical glass so-called a resonant type and accompanying light absorption, such as semiconductor-dispersed glass or nano metal particle-dispersed glass, its third order nonlinear optical effect is small. Therefore, in order to use such a nonresonant type third order nonlinear optical glass for an optical switch, it has been necessary to increase the device length or to increase the operation power. For example, when quartz glass is formed into a fiber and an optical switch is prepared therefrom, a switch operation (switching) in from 5 to 20 picoseconds is possible, but in order to obtain a practical optical switch, it has been necessary to make the fiber length to be about 1,000 m. Accordingly, also in the field of the nonresonant type third order nonlinear optical glass, strenuous efforts are being made to develop a glass having a large third order nonlinear optical effect.
On the other hand, JP-A-3-21934 discloses that an As-S type glass known as chalcogen glass, has a large nonlinear optical effect, so that a high speed switching operation at the same level as a quartz glass fiber is possible with a length of about {fraction (1/1,000)} of the quartz glass fiber. However, chalcogen glass has had a problem such that it is necessary to control the atmosphere during the preparation of the glass, the process for preparing the glass tends to be cumbersome for the control of the discharge out of the system of As, Se, S, etc., or the glass transition temperature is low, the thermal stability is poor, and the optical damage threshold is inferior.
Further, as a wavelength-conversion fiber, a quartz fiber doped with germanium has been reported. However, the third order nonlinear optical effect is small, and to use it as an optical switch, it is still required to have a length of about 1,000 m.
It is an object of the present invention to provide a glass fiber which does not contain any one of As, S and Se and which can be prepared by a conventional process for preparing glass and wherein a glass having a large third order nonlinear optical effect is used as the core glass.
The present invention provides a glass fiber comprising core glass and clad glass, wherein the core glass consists essentially of from 25 to 70 mol % of Bi2O3, from 5 to 74.89 mol % of B2O3+SiO2, from 0.1 to 30 mol % of Al2O3+Ga2O3, and from 0 to 10 mol % of CeO2.